Composite high strength machine element and method of making the same

ABSTRACT

This composite high-strength bushing consists of a heavy-loadbearing sleeve of sintered powdered high-performance alloy and a lesser-load-bearing support sleeve of sintered base metal such as sintered powdered iron. The outer sleeve has an internal taper while the inner sleeve has a matching external taper, both sleeves being separately formed from their respective powdered metals by suitable dies in conventional briquetting presses and thereafter sintered and forged by forcing them together in a hotforging press at a high temperature. The outer and inner sleeves are thereby firmly and inseparably joined by high heat and pressure and interlocked by the migration of minute portions of one of the metals past minute portions of the other metal across the tapered interface therebetween, thereby forming an intermediate zone of the intermingled metals encircling the interface. A modification employs tapers of slightly different convergence between the outer and inner sleeves but also results in a similarly-inseparable interlocking connection by a similar migration of the metals into an intermediate zone encircling the interface.

United States Patent 1 1 Dunn [75] Inventor: William M. Dunn, Farmington,

Mich.

[73] Assignee: Federa1-Mogul Corporation,

Southfield, Mich.

[22] Filed: June 14, 1971 [21] App]. No.: 152,862

[52] 11.8. CI. 29/191, 29/196.1 [51] Int. Cl. 1504c 2/08 [58] Field of Search 29/196.3, 191, 196.1, 29/191.2, 420.5, 474.3; 75/208, 123 J [56] References Cited UNITED STATES PATENTS 3,189,988 6/1965 Crane l. 29/420.5 2,326,730 8/1943 Kelly et al. 29/196.1 2,753,859 7/1956 Bartlett 29/420 UX 2,913,819 11/1959 Andreotti et al. 29/420.5 1,745,612 2/1930 Elmen 75/123 J UX 2,747,261 5/1956 Stosuy... 29/191.2 3,409,966 11/1968 l-Iilbish 29/196.1 X

FOREIGN PATENTS OR APPLICATIONS 369,964 3/1932 Great Britain 75/208 X 628,679 9/1949 Great Britain 75/208 R Primary Examiner-A. B. Curtis Attorney-Barthel & Bugbee [57] ABSTRACT This composite high-strength bushing consists of a heavy-load-bearing sleeve of sintered powdered high performance alloy and a lesser-load-bearing support sleeve of sintered base metal such as sintered powdered iron. The outer sleeve has an internal taper while the inner sleeve has a matching external taper, both sleeves being separately formed from their respective powdered metals by suitable dies in conventional briquetting presses and thereafter sintered and forged by forcing them together in a hot-forging press at a high temperature. The outer and inner sleeves are thereby firmly and inseparably joined by high heat and pressure and interlocked by the migration of minute portions'of one of the metals past minute portions of the other metal across the tapered interface therebetween, thereby forming an intermediate zone of the intermingled metals encircling the interface. A modification employs tapers of slightly different convergence between the outer and inner sleeves but also results in a similarly-inseparable interlocking connection by a similar migration of the metals into an intermediate zone encircling the interface.

3 Claims, 11 Drawing Figures INVENTOR FIG. 5

WILLIAM NI. DUNN SHEET 10F 4 BY flax/(Z4 1 v W ATTO NEYS F I G 5 S/NTER aura? SLEEVE l/VTER MIA/ER SLEEVE FIG.4

av/E775 PATENTEDUET 2 3,762,881

SHEET 20F Q F K5. 7 INVENTOR WILLIAM M. DUNN lav/3411M? ATTORNEYS PAIENIED 21975 3,762,881

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INVENTOR WILLIAM M. DUNN B Y @WYW L ATTORNEYS COMPOSITE HIGH-STRENGTH MACHINE ELEMENT AND METHOD OF MAKING THE SAME In the drawings,

FIG. 1 is a longitudinal section through the outer powdered metal sleeve, after briquetting and sintering, according to one form of the invention;

FIG. 2 is a longitudinal section through the inner powdered metal sleeve, after briquetting and sintering, according to the same form of the invention;

FIG. 3 is a longitudinal section through a hot-forging die in a hot-forging press, showing the outer and inner sleeves of FIGS. 1 and 2 at the start of the hot-forging operation of uniting them into a composite bushing;

FIG. 4 is a longitudinal section through the composite bushing, after forging;

FIG. 5 is a flow diagram of the steps involved in the method of making the composite bushing of FIG. 4;

FIG. 6 is a longitudinal section through a modification of the invention shown in FIGS. 1 to 5 inclusive, wherein the outer and inner sleeves possess slightly different converging tapers, with the components assembled immediately prior to hot forging as in FIG. 3;

FIG. 7 is a photomicrograph of a longitudinal section of the composite bushing of FIG. 4 showing the interlocking of the different metals at the interface;

FIGS. 8 and 9 are reproductions of graphical test charts produced by tension tests made upon specimens cut from the composite bushings, as shown in FIG. 4;

FIG. 10 is a photomicrograph similar to FIG. 7 but showing the interlocking of the metals of the different metals at the interface of a longitudinal section of the modification involving the differently-tapered sleeves shown in FIG. 6, after hot-forging; and

FIG. 11 is a longitudinal section through the composite bushing, after forging, with the positions of the com ponents of FIG. 4 reversed.

Referring to the drawings in detail, FIG. 4 shows a composite high-strength bushing, generally designated 10, according to one form of the invention, as composed of a high-performance alloy outer sleeve 12 joined at an approximately conical or tapered interface 11 to a plain iron inner sleeve 14 with opposite flat annular end surfaces 13 and 15. The sleeves l2 and 14 are formed from sintered powdered metal outer and inner components 16 and 18 respectively (FIG. 3) according to the procedure shown in the flow chart or diagram in FIG. 5. The outer and inner components 16 and 18 (FIGS. 1 and 2) are formed by briquetting a suitable high performance alloy and iron respectively in the die cavities of conventional briquetting presses (not shown), each having a core rod and upper and lower punches, by briquetting procedures well known to those skilled in the powdered metallurgy art. The dies for briquetting the outer components 16 are so formed as to impart to the outer component 16 an outer cylindrical surface 20, upper and lower annular surfaces 22 and 24, a relatively short upper inner cylindrical bore surface 26, and a lower tapered or conical bore surface 28, with the surfaces 26 and 28 collectively forming a partially tapered and partially cylindrical inner surface 30.

The dies for briquetting the inner component 18, on the other hand, are so formed as to provide an outer surface 32 consisting of a relatively short lower cylindrical surface 34 and an upper conical or tapered surface 36, the surface 36 having the same taper as the surface 28 of the outer component 16. The short cylindrical surfaces 26 and 34 provide clearances with the adjacent tapered surfaces 36 and 28 respectively. These clearances receive the sidewise flow of metal during forging and thereby prevent folding over" at the opposite ends 13 and 15. The inner component 18 has upper and lower flat annular surfaces 38 and 49 respectively and an inner cylindrical surface 42. The outer component 16 is formed by briquetting a powder of a suitable high performance metal or metal alloy, the particular alloy being used as exemplary in the present invention being the so-called S.A.E. 4600 alloy powder. The inner component 18, which does not require the load-bearing characteristics of the outer portion 12 of the composite sleeve 10, is formed from plain iron powder. The tapered surfaces 28 and 36 are both formed with matching tapers of 3. Briquetting is carried out to produce a density of approximately percent in the finished briquettes I6 and 18. Separate sintering is then carried out at a temperature between 2,100 and 2,150 F., individually for each piece.

The sintered powdered metal outer and inner sleeves l2 and 14 are then placed in telescoped relationship, the temperatures of both components are then brought to a predetermined forging temperature within the range of l,500 to 2,100" F. and then placed in the cylindrical die bore 42 of a forging press 44. The latter is provided with a hot-forging die set 45 including a die plate 46 containing the cylindrical die bore 42, a lower tubular punch 48 and an upper tubular punch 50 adapted to telescope with the die bore 42 and having flat annular facing surfaces 52 and 54 respectively adapted to produce the flat annular end surfaces 13 and 15 respectively in the composite high strength sleeve or machine element 10 (FIG. 4). The lower tubular punch 48 (FIG. 3) is provided with a cylindrical bore 56 while the upper punch 50 is provided with a cylindrical bore 58 of the same diameter formed within a tubular lower portion 60 depending from a main ta pered upper punch portion 62. A cylindrical core rod 64 with an outer cylindrical surface 66 is adapted to telescope with the lower and upper punch bores 56 and 58 and with the die bore 62 to define a die cavity 68.

In carrying out the method (FIG. 5) of making the composite high-strength machine element 10 of FIG. 4, the outer high performance alloy component 16 and the inner low performance component 18 are separately briquetted to densities of approximately 75 percent in separate briquetting dies to produce the configurations described above. The briquettes 16 and 18 (FIGS. 1 and 2) are then separately sintered at temper atures preferably between 2,l00 and 2,150 F. with the upper tubular punch 50 retracted upward so as to leave the mouth of the die cavity 68 open. The sintered outer and inner sleeves 12 and 14 are then removed from the sintering oven and transferred to the die cavity 68 of the forging die set 45 of the forging press 44 at a predetermined temperature between l,800 and 2,l0O F. alternatively, it may be more convenient to reheat the sintered sleeves l2 and 14 prior to placing them in the forging die cavity 68, due to loss of heat sustained in making the transfer from the sintering oven to the forging press 44. The thus heated sintered outer and inner sleeves 12 and 14 are placed in the forging die cavity 68 in telescoping relationship (FIG. 3). The upper punch 50 is moved downward with the cylindrical surface 42 of the die plate 46 preventing lateral metal flow and the top surface 52 of the lower punch 48 acting as an anvil to effect axial motion of the outer sleeve 12 relatively to the inner sleeve 14. This hot forging operation is carried out with sufficient force to drive the outer sleeve 12 with the internal tapered surface 28 of the outer component 16 axially downward upon the outer tapered surface 36 of the inner sleeve 14 and to raise the density of the composite element to about 98 percent, or substantially solid metal. This action causes the end surfaces 22 and 24 of the outer sleeve 12 to move into substantially co-planar relationship with the end surfaces 38 and 410 respectively of the inner sleeve 14 (FIG. 4). This relative axial motion between the tapered surfaces 28 and 36 of the outer and inner sleeves l2 and 14 under the effect not only of the initial heating of the outer and inner sleeves 12 and 14 but also that generated by the force of compression, causes a scrubbing action at the interface 11 which results in an excellent and continuous welding between the two sleeves 12 and 14 and produces a migration of the metals of the two sleeves 12 and 14 across the interface 11 into an intermediate zone of intermingled metals encircling the interface 11 and which results in an inseparable and continuous interlocking thereof along the interface 11, as shown by the photomicrograph (FIG. wherein the light-colored portion is the high strength alloy and the dark-colored portions the iron.

Torsion tests (FIGS. 8 and 9) of standard specimens cut longitudinally from the composite bushing 10 at the interface 11 therebetween confirm the exceptional interlocking obtained at the interface 11. These specimens comprised rectangular blocks one inch in length and 0.312 inches square with the interface 11 disposed midway between the longitudinal side surfaces. The tests were performed in the torsion testing machine disclosed and claimed in the l-laller US. Pat. No. 3,122,915 of Mar. 3, 1964 for Torsion Testing Machine. In these two graphic charts, the abscissae represent the applied twist to the specimen in degrees whereas the ordinates indicate the applied torque in inch pounds. The curves obtained were drawn by a pen moving transversely to the motion of the chart. The peaks of the curves A, B, C, D and E represent the peak torque measured in inch pounds obtained when the test specimen began to fracture or fail, and the rotation or twist of the test specimen in degrees at which such failure occurred is indicated by the reading of the horizontal scale designated by the words twist (degrees)". Thus, it will be seen that test specimen A failed after a rotation of 82 at a peak torque of 545 inch pounds, specimen B after a rotation of 82 at a peak torque of 540 inch pounds, specimen C after a rotation of 94 at a peak torque of 540 inch pounds, specimen D after a rotation of 101 at a peak torque of 555 inch pounds, and specimen B after a rotation of 85 at a peak torque of 500 inch pounds.

Long experience and extensive experimentation with the torsion testing machine identified above prove that empirical formulae could be developed which would employ the results of experimental tests to indicate the tensile strength and the percentage of elongation for a given rotation which could be expected in such test specimens. These empirical formulae are as follows: Tensile strength (lbs. per square inch) peak torque (inch pounds)/0.007 Percentage of elongation peak rotation (degrees)/5 Thus, the estimated tensile strength for specimen A is 77,850 p.s.i. with 16.4 percent elongation; for specimen B a tensile strength of 77,143 p.s.i. with 16.2 percent elongation; for specimen C a tensile strength of 77,143 p.s.i. with 19 percent elongation, for specimen D a tensile strength of 79,286 p.s.i. with 20 percent elongation; and for specimen E a tensile strength of 71,430 p.s.i. with 17 percent elongation.

By forging the modified construction shown in FIG. 5 in the die cavity 68 of the die set 45 of the forging press 44, according to the same procedure described above, there is produced a composite high-strength bushing 71) which is substantially identical in appearance to the composite high strength bushing 10 shown in FIG. 4, hence is not separately illustrated in its finished form. The sole difference in the construction is that the composite bushing, generally designated 70, consisting of the outer sleeve 72 of high performance alloy with the inner sleeve 74 of base metal, such as plain iron, brings together differently tapered internal and external conical surfaces 76 and 78 of the outer and inner sleeves 72 and 74 respectively. In particular, the internal conical surface 76 of the outer sleeve 72 is provided with an approximately three-degree taper, whereas the outer conical surface 78 of the inner sleeve 74 is provided with a two-degree taper. The briquett ing, reheating, sintering and forging procedures, includingthe temperatures and pressures involved, remain substantially the same as those set forth above in connection with the production of the composite high performance bushing 10 of FIG. 4 and achieve similar results. A similar interlocking at the interface corre sponding to the interface 11 is also produced, with a similar migration of the two metals into one another at that interface, as shown by the photomicrograph in FIG. 10. Torsion tests of the modified construction of FIG. 6 using converging tapers instead of identical tapers also resulted in no failures along the interface but where the test was carried out to the point of failure or rupture, such failure occurred at locations other than at the interface, in a manner similar to results of the torsion tests of the form of the invention shown in FIG. 4.

The above-mentioned nickel-content S.A.E. 4600 iron alloy powder has the following composition:

manganese 0.20%

with the remainder iron, plus nickel 1.75%

carbon to suit molybdenum 0.25%

The nickel-free high-performance iron alloy powder also mentioned above has the following composition:

manganese 0.48% with the remainder iron, plus nickel none% high carbon 0.59% or low molybdenum 0.59% carbon 0.28%

Heat treatment of the composite bushing 10 or is carried out in the usual and customary manner. It will of course be understood that the word iron as used herein includes iron having carbon therein for controlling the hardness desired,'as achieved by such heat treatment. It also includes carburization for providing a hardened external surface, such as by case hardening.

In a further modification of the invention, FIG. 11 shows a composite high-strength bushing, generally designated III), as consisting of a reversal of the components shown in FIG. 4, namely as composed of an iron outer sleeve I12 joined at an approximately conical or tapered interface 114 to a high performance alloy inner sleeve 1116 with opposite flat annular end surfaces 118 and 120. The sleeves 112 and 116 are formed from sintered powdered iron and high perfor mance alloy outer and inner components shaped like the components 16 and 18 (FIG. 3) according to the procedure described above for producing the composite high-strength bushing of FIGS. 1 to 4 inclusive shown in the flow chart or diagram of FIG. 5. Accordingly, it is believed that no further explanation is needed. It will be understood that the composite bushing 10 of FIG. 4 is suitable for the inner race ofa roller bearing, whereas the composite bushing 110 is suitable for the outer race thereof, with conventional cylindrical rollers disposed in the annular space therebetween. It will also be understood that the modified composite bushing 110 is suitable for use as a high performance plain sleeve bearing for rotatably supporting a shaft (not shown) in its bore 122 while its outer cylindrical surface 124 is mounted in the usual counterbore or seat in the machine frame or other supporting structure (not shown).

I claim: I. A composite high-strength bushing comprising an inner sleeve of a base sintered powdered metallic material having a tapered external surface thereon. and an outer sleeve of a high-strength powdered metallic material having an internal bore tapered correspondingly to said tapered external surface and fusibly joined thereto in snugly-fitting telescoped mating engagement with said tapered external surface at a substantially frusto-conical interface therebetween, minute portions of one of said metallic materials extending irregularly past minute portions of the other of said metallic materials across said interface into interlocking engagement with one another in anintermediate zone encircling said. in terface and containing the thus intermingled metallic materials, said base material being iron and said high-strength material being a manganese'molybdenum iron alloy.

2. A composite high-strength bushing, according to claim 1, wherein said high-strength material is a nickelcontent manganese-molybdenum iron alloy.

3. A composite high-strength bushing, according to claim ll, wherein said high-strength material is a nickel free manganese-molybdenum iron alloy. 

2. A composite high-strength bushing, according to claim 1, wherein said high-strength material is a nickel-content manganese-molybdenum iron alloy.
 3. A composite high-strength bushing, according to claim 1, wherein said high-strength material is a nickel-free manganese-molybdenum iron alloy. 